Inhalation therapy is the cornerstone of asthma treatment, used for the delivery of 'reliever' bronchodilator therapy (e.g. salbutamol) as well as anti-inflammatory corticosteroid 'maintenance' or 'controller' therapy. Currently available inhaler devices include MDIs, breath-actuated MDIs (BAIs), and dry powder inhalers (DPIs). Both BAIs and DPIs are actuated by the patient's inhalation manoeuvre, while MDIs are actuated by the patient's pressing of a button, which must thus be coordinated with inhalation. The clinical effectiveness of inhalation therapy derives from delivery of drug to the target sites in the lungs, and evidence is mounting that suboptimal use of inhaler devices is a common problem contributing to compromised asthma control for many patients. Indeed, decreased asthma control has been linked to the number of mistakes when using MDIs for delivering inhaled corticosteroids (ICS).